The invention relates to a process and a plant for separating a feed mixture predominantly or exclusively containing carbon monoxide and hydrogen in which the feed mixture is subjected to a cryogenic separation process in which a carbon monoxide-rich liquid and at least one residual gas mixture which is depleted in carbon monoxide and enriched in hydrogen, in comparison with the feed mixture, are formed.
High-purity carbon monoxide is usually obtained by means of cryogenic separation processes from synthesis gas that is customarily prepared via a catalytic conversion, partial oxidation, autothermal reforming and/or steam reforming of coal or coke, natural gas and/or hydrocarbonaceous feeds.
In EP 0 130 284 A2, a process is described for obtaining pure carbon monoxide from a feed mixture that still principally contains hydrogen and carbon monoxide after other components such as methane and nitrogen are separated off. The feed mixture is compressed, freed by adsorption from carbon dioxide and water that are still present, and cooled until the predominant part of the carbon monoxide has condensed. The remaining gaseous fraction is warmed and given off, and the condensed carbon monoxide is expanded for outgassing hydrogen that is dissolved therein. One part of the remaining carbon monoxide is vaporized, and one part is delivered as product.
A process of the type described therefore comprises a cryogenic separation process having a first separation step and a second separation step. In the first separation step, the predominant part of the carbon monoxide is condensed out, with non-condensed residue remaining (customarily designated “crude hydrogen”, in the context of the present application, also as “first” residual gas mixture). In the second separation step, the condensed carbon monoxide is expanded in such a manner that the dissolved hydrogen outgasses and a further gas mixture is formed thereby (usually denoted “flash gas”, in the context of the present application, also as “second” residual gas mixture).
The first residual gas mixture formed in the first separation step still contains considerable amounts of carbon monoxide. In conventional processes, this first residual gas mixture is passed out of the process. The carbon monoxide present in the first residual gas mixture is therefore lost. Also, in the second separation step, certain amounts of carbon monoxide are transferred to the gas phase. In the second residual gas mixture also, therefore, not inconsiderable amounts of carbon monoxide are present. The content of carbon monoxide in the second residual gas mixture corresponds to the equilibrium at the top of a stripping column used in this case. Such carbon monoxide is also to be considered as a loss in conventional processes. The said losses in carbon monoxide decrease overall the carbon monoxide yield of a corresponding process or of a corresponding plant.
Against this background, the present invention sets itself the object of specifying a process and a plant for the separation of a feed mixture predominantly or exclusively containing carbon monoxide and hydrogen, by means of which process or plant the carbon monoxide losses explained may be decreased and thus higher carbon monoxide yields altogether may be achieved.